The Collaborative International Dictionary of English v.0.48:

Hyson \Hy"son\, n. [Chin. hi-tshun, lit., first crop, or
   blooming spring.]
   A fragrant kind of green tea.
   [1913 Webster]

   Hyson skin, the light and inferior leaves separated from
      the hyson by a winnowing machine. --M`Culloch.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hyson
    n 1: a Chinese green tea with twisted leaves